Lima, Lonetá L., [email protected] Zavaglia, Cecília A.C., [email protected] Faculty of Mechanical Engineering – FEM/UNICAMP; National Institute of S&T in Biofabrication (INCT-BIOFABRIS), Campinas - São Paulo/ Brazil.
Bavaresco, Vanessa P., [email protected] CTC – State University of Campinas, National Institute of S&T in Biofabrication (INCT-BIOFABRIS), Campinas, São Paulo, Brazil .
Abstract. Cartilage is a type of dense tissue composed of collagen, elastic fibers and chondrocytes, embedded in a firm
gel. The cartilage provides rigidity to vertebrates body and in the human body presents in three different forms: elastic
cartilage, fibrocartilage and hyaline cartilage. These forms are due to fiber in the matrix, and due to the needs
biomechanical (resistance to mechanical stresses and flexibility) to the locations where they are located. The
pathologies in the cartilage of the joints interfere with movement and mobility, causing pain and many hardships for
patients. A biomaterial to be used as artificial cartilage it should present similar mechanical behavior of cartilage:
resist compression, possess the ability to exude fluids that act as a lubricant between the surfaces in contact, and
provide resistance to shear movement. Among the options available poly vinyl alcohol (PVA) is studied by presenting
these biomechanical characteristics. In this work was produced six membranes of PVA (MM 89000-98000) 15%: 3
membranes were prepared using 1% of the thermo initiator potassium persulfate (KPS) (w / v) and 3 membranes with
1% 4,4- Azobis (4-Cyanovaleric acid) ( Azobis) (w / v). After thermal crosslinked processes the morphology of the
membranes were analyzed by scanning electron microscopy (SEM) and optical microscope (OM) with polarized light,
was possible to visualize the difference in coloration and structure of membranes. The thermal behavior of membranes
were analyzed by differential scanning calorimetry (DSC) using two heating steps. The first using temperature between
25 ° until 250 ° C, after cooling until 0ºC and the second heating since 0ºC until 300ºC , the rate 10 º C / min in N 2
atmosphere, in this study was possible to identify the peak of glass temperature (Tg) and the melting temperature
(Tm) peaks, in the membrane produced to azobis initiator. The membranes produced with KPS presented only graph
part of PVA crosslinked, the graph nothing presents the peaks of Tg and Tm. The membranes also were performed
testing fraction sol / gel , by heat of distilled water at 85 ° C for 3hours. The membranes produced with KPS not
dissolved in this condition, but the membranes produced with Azobis dissolved into parts. Through this study it was
possible to verify that the samples were thermal crosslinked using both thermo initiators.
One tool that can be used to produce of artificial cartilage is the rapid prototyping (RP). The RP is a technology
that allows construction of complex models with internal details that could not be manufactured by other
manufacturing methods. The models are constructed from a virtual model obtained by 3D CAD, computed tomography
scan , and among others. The RP has allowed construct the precise and detailed biomaterial to use in medicine, this
method is characterized by an additive process, where models are built layer by layer “Souza and Ulbrich (2009)”. The
RP has been developed to use in medicine because aims to produce the specific devices implantable for each patient.
In this work was studied the thermal crosslinking process of PVA with two thermo initiators (KPS and Azobis).
The PVA is a biomaterial that has been studied as replacements "plugs" implantable cartilaginous defect to stop the
advance of wear and prevent total disruption of the cartilage. The PVA hydrogel also have been studied for use as
wound dressing, the wound dressing are used to promote a physical barrier that prevents contamination of the wound by exogenous organisms, thereby facilitating healing and minimizes the scar production “Liu et al.(2010)”. During the
wound healing process, the biomaterial should have antifungal and bactericidal character; permeability of oxygen; and
the capacity of adapt to the countour of deep or irregularly shaped of wounds “Sirousazar and Yari (2010)”.
The KPS is a strongly oxidizing radical producer, and promotes coupling between polymer radicals leading to a
crosslinked structure “Bolto et al. (2009)”. The KPS is most used like initiator for polymerization in aqueous medium.
It is generates sulfate ion radicals by it is thermal or photochemical decomposition. The persulfate ion induces a radical
on the PVA back bone chain and the vinyl monomer. As possible that it can oxidizing some of the generated radicals
(secondary alcohol) into carbonyl group “Gholap, Jog and Manohar (2004)”. Using the Azoinitiator is possible to
produce free radical polymerization, the polymerization reaction occur due to rate temperature “Lyoo et al. (2006)”.
The structure of PVA is usually crystalline due to the strong intermolecular interaction between PVA chains with
intermolecular hydrogen bonding. The intensity of peak in the diffraction graph and also the size of the crystals of PVA
are determined by the number of PVA chains packing together “Ma et al. (2002)”. In this study was analyzed the crystalline structure of PVA using the x-ray diffraction technique.
2. MATERIALS AND METHODS
2.1. Production and thermal crosslinking process in the membranes
In this work was produced six membranes of PVA (MM 89000-98000) 15%: 3 membranes were prepared using
1% of the thermo initiator KPS (w / v) and 3 membranes with 1% Azobis (w / v). The membranes were dried at room
temperature and then crosslinked with heating at about 120°C using a ventilated oven. The permanence times of the
membranes in the ventilated oven were: 3 hours, 4 hours “Fig. 1 (a , b)” , and 5 hours.
(a) PVA 15% +1% KPS (w/v) after 4H at 120ºC
(b) PVA 15% +1% Azobis (w/v) after 4H at 120ºC
Figure 1- Samples after 4 hours at 120ºC (a) Sample with KPS (b) Sample with Azobis – Images by digital camera.
2.2. Visual and morphology analysis
The samples were visual analyzed by photograph digital camera, model DSC-W35 Cyber-shot, Sony trademark;
scanning electron microscopy (SEM), JEOL trademark, model JXA 840A plus EDS Noram System Six, and optical
realized with distilled water heated at 85ºC for 3 hours. The PVA hydrogel was weighed and then immersed in distilled
water heated at 85ºC by 3 hours. After the extraction the specimens was removed, dried and reweighed. The amount of
gel extracted was calculated by “Eq. 1”.
Gel Content % = Wf / Wo (1)
Sol Content % = 1 – Gel Content
Where “Wo” is the original weight dry PVA, and “Wf “ is the weight of the PVA after extraction and drying.
2.4. Thermal analysis
The thermal analyses were realized by differential scanning calorimetric (DSC) technique, using equipment DSC
Mettler Toledo model 823e. The samples analyzed were heated and cooling: initially heat 25 at 250ºC, cooling 250ºC at
0ºC and after heat 0ºC at 300ºC.
2.5. Analysis of crystallinity
For the analyses of x-ray diffraction were used the equipment Rigaku trademark, model DMAX 2200, with radiation
CuKα, filter of Ni, 20kV, 20mA. Was used step of 0,02° and time of integration of 1s.
3. RESULTS AND DISCUSSIONS
3.1. Morphology analysis
After the thermal crosslinking processes the morphology and appearance of samples become differences, the
samples produced with KPS were dark coloration, and the thermo initiator Azobis produced the milky color in the
samples “Fig. 2”
In the (OM) with polarized light was possible to visualize the difference in the structure of membranes. The visual appearance of the 6 membranes are like a brittle material, but the three membranes that were produced with the KPS are
more brittle than those produced with Azobis.
(a) Sample with KPS magnification 100x – (OM) (b) Sample with Azobis magnification 100x – (OM)
Figure 2 – Membranes of PVA 15% + 1% of thermo initiators after thermal crosslinked process – (OM) (a) KPS (b)
Azobis.
In the (OM) the samples were visualized with polarized light, was possible to view the presence of thermo initiator
in the matrix of PVA.
Proceedings of COBEM 2011 21st Brazilian Congress of Mechanical Engineering
Through this study it was possible to verify that the samples were thermal crosslinked using both thermo initiators.
The KPS thermo initiator was more efficient in the thermal crosslinking process, the Azobis crosslinked only parts
of PVA. But as the samples were brittle couldn’t be used as a medical device for treating cartilage. The samples can be
used like dressing wound , because nothing presents the mechanical resistance necessary to applied like medical device
for treatment for cartilage.
5. ACKNOWLEDGEMENTS
The agency of foments - Capes, and the INCT Biofabris.
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7. RESPONSIBILITY NOTICE
The following text, properly adapted to the number of authors, must be included in the last section of the paper: The authors Lonetá Lauro Lima, Cecília Amélia de Carvalho Zavaglia and Vanessa Petrilli Bavaresco are the only
responsible for the printed material included in this paper.
